Question : How long do most people stay in Osaka when they fly in from Jeddah?
Answer : Of course you're not most people, but if you were, you'd stay roughly 21 days.
Question : Would you be willing to change your travel days if it saved you money?
Answer : For the month of December, the cheapest day to fly is Sunday. Being flexible with your travel days garners you even more savings during your booking.
Question : Are prices changing frequently for this route?
Answer : Prices for this trip tend to change much more than others. However, the sooner you book, the better price you tend to get.